This invention relates to formation of lateral nipples on tubular stock, and particularly to forming nipples on configurated, stainless steel, engine manifold bodies, for cooperative interfit of the nipples with side runners.
In years past, engine manifolds were largely made of heavy cast construction. In recent years, technological developments have enabled manufacture of engine manifolds from stainless steel tubular stock. In so doing, the side members, called runners, are welded onto the main body, called the "log", around openings laser-cut into the body in accordance, for example, with the teachings of U.S. Pat. No. 4,644,128 issued Feb. 17, 1987. Typically, the body or log is of unusual configuration, having portions at angles to each other, while the runners are attached to and project laterally from these portions at various acute angles. If the runners are butt welded to the log, subsequent flexing and/or vibration of the runners during use can result in cracking at the welds. Moreover, exhaust turbulence is created at the juncture of the components, causing localized hot spots with concomitant stresses and potential joint failure.
While it would be advisable to have the runners lap welded into integral nipples protruding from the body, instead of butt welded to the body wall, the fact that the body is of stainless steel and therefore difficult to form, the fact that the body typically has a peculiar configuration, and the fact that the runners project at acute angles to the body have effectively limited this type of arrangement. Specifically, it has not been practical to properly form the necessary nipples on a production basis. One technique which has been proposed is to spin form nipples. However, this works only for nipples at 90 degrees to the body, on round holes, and is time consuming and considered too costly. Basically this technique is not practical for most stainless steel engine manifolds, which require runners at differing angles and extending from portions of the manifold at angles to each other.
Another technique employed to some extent has been to cause the mouth of each runner to be flared to extend over a considerable portion of the body around the precut opening in the body. However, this technique has disadvantages including potential localized hot spots caused by turbulence of hot exhaust gases flowing from the runners and striking the protruding body portions within the flared runner mouths. Hot spots tend to cause uneven stresses and subsequent failure, as is known.